


A Love Song by the Ocean

by Butterfly_chic21



Category: Gravity Falls
Genre: Arranged Marriage, Crossdressing, Eventual Romance, Eventual Smut, F/M, Falling In Love, Human Bill Cipher, Kidnapping, M/M, Pirate Bill Cipher, Siren Dipper Pines, Siren Mabel Pines, Siren Princes and Princesses, Trans Dipper Pines, siren songs
Language: English
Status: In-Progress
Published: 2019-12-11
Updated: 2020-03-31
Packaged: 2021-01-31 18:55:20
Rating: Mature
Warnings: Graphic Depictions Of Violence, No Archive Warnings Apply
Chapters: 3
Words: 3,195
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21451078
Author URL: https://archiveofourown.org/users/Butterfly_chic21/pseuds/Butterfly_chic21
Summary: In the reef of Gravity Falls, on their 18th birthday Dipper and Mabel Pines will be marriage to one of the suitors in the kingdom or in the neighbored kingdoms. At the last minute Dipper leaves her home and gets kidnapped by a Golden Captain.
Relationships: Bill Cipher/Dipper Pines, Mermando/Mabel Pines
Comments: 5
Kudos: 75





	1. Worst Birthday Ever

(❊)

In the depths of the deep blue sea. Lays a group of five kingdoms. In the center of these five kingdoms was the kingdom of Gravity Falls. The kingdom is rule by Michael and Michelle Pines who also had two children, Mabel and Mason. Princess Mabel the eldest, as going to be married to one of the kingdoms suitors and become queen in the kingdom that her suitor is from. Prince Mason the youngest, will also be wedded to one of the suitors of the five kingdoms and ruled the Gravity Falls kingdom as Queen. This won’t happen until the twins 18 birthday which is today. 

Michelle swam to her son’s bedroom holding a gift for his birthday. A gold crown that had been in the family for generations. 

When she arrives at the young prince’s chamber door, she knocks on the door. 

  
“Mason. Happy Birthday.” She says sweetly.   
  


The Queen opens the door to find an empty chamber.

"Mason?"

She drops the present on the ground and rings the bell warning the whole castle that the prince is missing.   
  


The king watched the whole castle guard send out search parties and went into a frenzy trying to find his son. He shook his head.   
  


“Not again.” He sighed,   
  


Dipper was swimming with some colorful angel fish. Until a rather sparkly object caught his eye. He swam to the cave and found the object. A shimmering pink underwater rose. He eyes studied the plant for a moment before he put in in his pouch. He swam out of the cave and headed to his hideout. The prince arrives at an cove with old treasures that was hidden behind a rock wall. Dipper pulled out the the flower and a mysterious journal. He gets a pen and begins to speak as he writes.

"Today, I found a shimmer pink rose. I believe it might be the rosea ignis flower. Which gives merpeople the power to create pink flames when eaten and when the petals are smashed it creates a potion of healing properties. I will either eat or create another potion."

Dipper place his journal down and grab the flower. 

"Well here goes nothing."

He open his mouth nearly putting the flower in. Until he's pet otter Orion comes in yapping. Startled by his loyal pet Dipper drops the flower on the ground. 

"Orion! What's the matter?"

Orion stops barking and points one of his flippers outside indicating to his master to listen. Dipper listen and he heard the bell.

"Uh oh. Come Orion. I guess my experiment has to wait." He sighed, he grabbed his pouch and swam out. He swam on his way to a ancient garden that he told his parents he would always be if he was feeling a bit stress. Unfortunately, he didn't make to the garden, he was caught by his Grunkles. Stan was the High Royal Guard, and Ford was the High Mage. 

"Hey Grunkle Stan and Grunkle Ford, how's it going." 

Neither males laugh or smile. Dipper put his head down and sighs. He lift his arm up and Grunkle Stan grabbed it dragging him back to the place. Ford was behind Dipper making sure he didn't escape. 

Once the three men arrived at the palace's throne room where they meet the annoyed King, anxious Queen, and the worried princess. 

"We found him near the octopus grove." Said Ford

The Queen rushed over to hug her son. Once Stan let his arm go.

"Mason, we were worried sick! How many must we tell you you can't leave this castle without your father and I's permission."

"Mom, I was perfectly fine. I just wanted to explore the sea."

"Mason, you know very well that explore beyond the Seahorse cove is strictly forbidden!"

"Grunkle Ford does it. Why can't I!"

"Mason, I'm a mage you're a prince. It's my duty to see what's going on beyond the city limits."

"I'm tired of being cooped up in these walls! I have excelled at all my studies and read every book on mystical creatures, fighting techniques, and everything a prince should know! I am perfectly able to go past the city limits!"

"**THAT'S ENOUGH!" **Shouted his father

"You are grounded young man! Your room will be surround by guards and guard will escort you everywhere." 

"But.."

"**NO!** You need to learn not dismiss our rules!"

"Mom, tell dad that this is not fair." Dipper whined

The Queen looked away, "I think it's for the best."

"Mabel, Grunkle Stan, Grunkle Ford. Please defend me." Dipper begged

Mabel looked away with sorrow, she couldn't go against her parents not now.

"Kid, you don't know what's out there. Staying behind these castle walls is for your safety." Said Stan

"I agree with your father. We need to ensure your safety which no more exploring." Said Ford

Dipper stare at his family in horror. 

"I HATE BEING A PRINCE AND I HATE THIS FAMILY!!! I CAN'T BELIEVE MY FAMILY WOULD DO THIS ON MY BIRTHDAY!" He screamed with tears.

Dipper swam away crying with Orion following. Mabel look her brother's figure with sadness.

This was the worst birthday ever.

(❊)

In Dipper's chamber, 

Dipper was crying on his bed. Orion was comforting him. 

"Oh, Orion. Why must my parents treat me like I'm a baby." 

Orion cuddled his neck and licked his face. 

Dipper held the pup close and cuddled him back. Until a knock was heard.

"Go away please."

"Bro-bro it's me. Can I come in." Said Mabel

Dipper swam to the door and opened it. Mabel and her pink otter Waddles came in. Dipper close the door behind her.

"Dipper, I'm so sorry I didn't defend you. I just couldn't."

"Why not? You're my sister we are supposed to have each other's back."

"Dipper, Mermando proposed to me. I have to be on Mother's and Father's good side or else I will be marrying somebody else."

"I didn't know, I'm sorry for getting anger at you. Congratulations on your engagement."

"Thank you. I have something that will cheer you up."

"What will that be?"

Mabel handed him a small box that she hid in her hair. Dipper opened it inside was a heart necklace. 

"The heart was the only one left so I grabbed it before my date with Mermando. The Jewelry woman says there enchanted to always know when your love one is safe. I thought it would be a symbol of our relationship as siblings."

"Oh Mabel, I love it." Dipper said as he put it on.

"There's something else. It's not a very nice present but I telling as a warning. Gideon Gleeful has proposed your hand for marriage and...mom and dad accept his proposal."

Dipper's eyes were wide as the giant squid's eyeball.

"I rather died than to marry that country idiot." He said with malice

"Dipper you don't have a choose. Our "parents" accepted his proposal. He wants to get married as soon as possible. In a couple of weeks you'll have your wedding."

"I don't believe this!"

"I tried to reason with mom and dad but two weeks is the latest they would push the wedding to. I'm sorry Dipdot."

"Thanks for trying Mabel. It's fine."

Mabel made her way out of Dipper's room. Sighing sadly as she closed the door.

"Oh Orion, this is the worst birthday ever."

Dipper cried all night.

(❊)

**Notes for the Chapter:**

> I’m done with school for the semester! I’m going to update all my stories.   
Hope you like this new story!  
Loves


	2. Don't Touch

**Notes for the Chapter:**

> Welcome to the next chapter! 
> 
> Warning: Non-consensual touching

(❊)

The next day, 

The King and Queen invited Gideon for dinner, Dipper was dressed in the best gold bracelets, and wore his best crown. After the prince was done dressing, he was escorted into the throne room. He stood below his mother's throne waiting for Gideon's arrival.

"You'll love Gideon, I'm sure Mason!" Michelle exclaimed,

Dipper rolled his eyes, he doubt it. 

Gideon arrived, he bowed to the King and Queen. Dipper would admit Gideon did change, his appearance at least. Muscular but too muscular for Dipper's taste, long white pulled into a ponytail, same blue eyes, no country accent though, and a sliver tail.

"Your highness, Thank ya so much for the invitation."

Never mind, he still has that ridiculous country accent.

"It's our pleasure besides I have to get use to my future son-in-law." Said Michael chuckling

Dipper nearly gagged, when his father said son-in-law. Gideon made his way over to Dipper.

"You look beautiful as ever, my bride." Gideon said as he give Dipper's hand a kiss. 

"Thank you Prince Gideon." 

An hour later, everyone was in the dining room eating. Dipper was eating not listening to the conversation with Gideon and his parents. Just then, a finger stroke his private area. Dipper glared at Gideon hoping to stop his unwanted fingers. Gideon smirk, then the finger went down into the fold of his slit. The prince dropped his fork putting his hand on his mouth to hide his moan.   
  
Everyone stared at Dipper’s flushed face when the fork clacked against the plate.   
  
“Mason, are you alright?” Asked his Mother

Dipper nodded, he swam out of Gideon’s hold.   
  
“I’m just going to the bathroom.”

Dipper swam to the royal bathroom. He noticed his slit was leaking fluids, he quickly wiped the slightly puffy red folds. 

A knock was heard on the door.

"Who is it?" Dipper asked determining whether it was his sister or mother

"It's me, my lovely Dipper." Said Gideon

Dipper internally groaned,

"What do you want Gideon."

"I just came to check up on you, and to see if you need my assistance..."

"I'm good Gideon, please leave me." 

There was silence, Dipper assumed that Gideon left. He went out of the bathroom and swam into his bedroom. Mabel was there with just what he needed.

"Here's the cloth with sea cucumber. It should calm the hormones."

Dipper took the cloth and placed it on his arousal. He felt a surge of calm in his body. He sat down in his chair let the sea vegetable do it's job.

"Let me guess Gideon cause this."   
  
“Yes. Stupid idiot started touching me in my slit.”   
  


“That’s gross!”   
  


“I can’t do it Mabes. I can’t go back out there can you just tell them that I’m sick. I’m going to sit this one out.”   
  


“Okay, I’ll tell them. See you later.”   
  


Mabel left, Dipper couldn’t take it anymore. He needed to leave this place. He was going to leave tonight.   
  


He is NEVER coming back.

(❊)

* * *

**Notes for the Chapter:**

> Next chapter coming soon!


	3. A Siren on the ship?!

**Notes for the Chapter:**

> Guess who’s finally updating!  
Due to COVID outbreak I’m now on lockdown in my home until further notice.  
Please Please stay safe out there!  
Wash your hands!  
Anyway,  
Onwards to the chapter!

(❊)

It was the dead of night. Dipper put the last of his belongings into his a small seaweed satchel. 

  
He opened his window, he was about to swim out of his window, when Orion grabbed his tail. Dipper turned around and sighed at his friend. 

“I’m sorry Orion. I can’t stay here for one more second. I go mad.” He whispered, the pup whimpered. Dipper hugged the pet and swam out of his window. He looked at the otter standing in his window one last time.   
  
“Goodbye Orion.”   
  
The brown animal waved its paws goodbye as he saw his master leave. Dipper swam outside the kingdom gates, he looked at his home and swam away.

He never looked back.

* * *

Next morning on the surface of the sea,

A large ship was casting out nets to catch fish. Two crew men were pulling the nets back to the boat.

"Why are we the ones that search em' fish?" Asked the crew man with raven hair

"Because Paci-fire, we are the only ones dat c'tch dem nets." 

"But Hector, Xan and Kry 're way 'ronger tha' us. Why don't they do it?"

"These two ar' the muscles of the crew. Now shut up and hel' me with the nets."

Paci-fire and Hector started pulling in the fishing nets. Fishes fell on the deck, Hector started collecting them while Paci-fire finished pulling the net thru. 

"Man this is a lot of fish. We're gon'a be eatin good t'nigh."

"S're ar'." Hector pulled the entire net out of the water, his eyes widen as he saw the rest of the catch.

"H-Hector."

"Boss is gon'a be s're happy with this her'. We hav' a enou' fishes to feed the army."

"Hector."

"We gon'a eatin' like the General No'thwest him'elf."

Hector finally saw Paci-fire's ghost face. He raised an eyebrow. "Wh't's matt'r with ya?"

Paci-fire point to the net and Hector saw the thing that was scaring Paci-fire. He dropped the fish.

-

Tad Strange was minding he old business counting the gold that they had plunged last night from a merchant ship.

Being the Captain’s first mate was harder but he did enjoy it from time to time. He got up and put the money in secret cupboard. He is interrupted by a scared Hector.   
  


“Boss!!! Where’s the Boss?!” shouted The scaredy-cat Hector. 

  
Tad quickly covered his month with a scowl. 

  
“A’e ye mad! C’p’n has ‘n ‘ule! Don’ wak h’m ‘less b’n w’ve be in Davy Jon’ locker!”

"S'ry Tad, bu' it's a 'mportant!" 

He whispered in Tad's ear, and Tad's eyes widen.

He gasped.

\- 

Tad slowly opened the door of the Captain's chambers. The dark room smelled heavy of alcohol and little streams out light throughout the room. He slowly stepped in.

"C-C'p'n."

"Aye, Taddy aye we be'n docking yet?" Said a deep voice

"N-no."

Footsteps boomed in the room, the floorboards creaked as the steps got closer and closer to Tad.

C'p'n Bill Cipher step into a stream of light. Bill Cipher was a feared pirate by all. One look from his gold eyes could kill anything. His dark sun-kissed skin was made by the blood of his enemies. The long gold hair indicate how rich he had got over the years. 

"Then Taddy, y did ya wok me eh?" He said with a scowl. 

"A-a creature on ye deck." 

"What kind of creature?"

* * *

Dipper growled,

He knew better than to go up to the surface. He was just trying to help that school of Angel fish escape the nets. He would've never know that he would get capture by pirates.

He was still caught in the fishing net on the deck surrounded by crew with swords. The sun was beating down on his tail drying up his scales. He wanted to squirm back to the ocean before he dies.

He growled again when a man with blue hair poked him with a sword. The male was about to poke him again

"Poke me again and I'll feast on your flesh!"

The man pulled back, and dropped the sword.

"What do we 'ave ye?" Said a voice

The other pirates all looked up at a tall blonde man who was walking closer and closer to the scene.

Dipper tried to bare his teeth at the male as he got closer but the blonde's eyes screamed of domination. Dipper isn't the type of person to fall head over heels for a person much less a pirate but this guy was just so charming. Dipper's submissive side was screaming for the blonde to claim him. 

The blonde stared at the merman with curiosity. He grabbed the brunette's face, almost like he was searching for something. Bill let go with a smile. 

"I'm sure some merchant will pay dearly for your kind." 

Dipper growled, Bill laughed and walked away.

"Get a barrel and put him in the dungeon. We'll sell 'im once we've dock." 

"Yo heard the Cap'n, cut the creature out of the net. Teeth do the honors and Xan hold em down." 

Xanthar pinned Dipper to the floor and Teeth started to cut the net off Dipper. As soon as Dipper's tail was free it start to sizzle. Dipper's fins turned into small feet, the body of the tail turned into pale legs. Teeth stopped cutting and Xanthar called for Tad. 

The rest of Dipper's body sizzled and soon Dipper was a human. Dipper was appalled, this wasn't suppose to happen to mermaids when they stay in the sun too long. 

Tad walked closer to Dipper, Dipper started to cry. 

"What did you do to me?!" He cried, Pyronica falling into her mother instincts immediately. She took off the rest of the net and cradle the brunette trying to calm him down.

Tad was shocked, the boy was not ordinary person. Bill came back because of Dipper's cry. 

"What's go'n on ye?!"

Bill saw Dipper's nude form. He grabbed Teeth by the neck. 

"How man' 'imes 'ave I told u! DO NOT PUT THOSE LEAVES IN THE FOOD!!"

"Bill calm down! It wasn't ye weed who did 'his. I thin' the boy might' be half human half mermaid."

Bill let go of Teeth, he turned to Tad. 

"Wha do ya mean, he might' be a half n' half. Those kin' of beings don' exist!" 

"Perhaps someon' in his family mus' be human but turn to a siren afterwards. Sadly I don' know much of mermaids but I know someon' who can 'elp us." 

"Ahh Bleeding Heart's family. Alrigh' new orders! Pyra you are now in charge of the kid! Eve'one else get bac' to work!"

Dipper was carried by Pyronica to the guest room. She sat him down on the bed and left. Dipper explored his body. His chest had small mounds with nipples, his hips were slightly curvy, and where his slit used to be was covered by a mound of flesh. He touch one of the mounds on his chest. He tried to push the mound back inside his body but the flesh bounced back. 

Pyronica came back with some clothing she saw how scared Dipper was. She knelt down infront of the boy and laid the clothing next to him. 

"You alright hun?"

"What's happening to me?" Asked Dipper with tears in his eyes.

"I don't know but we knew someone that can help explain all of this. I'm Pyronica by the way." 

"I'm Dipper."

She grab a piece of clothing and started to put it on the boy. The piece of clothing looked like one of Mabel's special shells she wore only for Mermando. 

"Is this shells you're putting on me?" Dipper asked, 

"It's called a bra in the human world. It's to hold your breasts in place so they don't bounce all over the place." 

"Oh." 

"Arms up kid." 

Dipper put his arms up, she pulled a shirt over his head. 

"So, you're a mermaid."

"I'm a merman well a different type of merman. I'm was a prince until I ran away from my home."

"Why did you do that?" 

"I was forced to be married by a guy I didn't like." 

"I understand the feeling. I wasn't always a pirate but I've always dreamed of being one. Unfortunately, my folks had other plans for me. So I ran off and join Bill's crew. Stand up and hold onto to me."

Dipper stood up and Pyra put on loose pants on him. Dipper let go of Pyra and held onto his necklace that Mabel gave him. 

"Walk around the room so you can get use to your legs. I'll get you once dinner is ready." Said the pink haired girl as she walked out of the room. She closed the door. 

Dipper was left alone. 

He was never more scared of his new self.

(❊)

* * *

**Notes for the Chapter:**

> Somebody help me with Pirate talk cuz....I can't type right lmao!  
Anyway,  
See you on the next chapter  
Loves and Stay safe!


End file.
